During the early twentieth century, science fiction writers began to consider the possible alteration of human beings and other species, either through the natural alteration of genes or by the use of deliberate genetic engineering. Stories of mutated humans first became common in the 1930s pulp magazines and in the British scientific romances of the time, mutation often providing the justification for stories of supermen. Such narratives provide scientifically rationalized accounts of the transformation of human beings and nature, a theme of timeless fascination, as shown by the many examples in ancient mythology and earlier forms of fiction.
While narratives that depict unexpected and uncontrolled mutation (e.g. as a result of radioactivity from nuclear tests) are usually often pessimistic in their attitudes to science and technology, more optimistic (or at least ambiguous) attitudes are sometimes found in narratives that deal with the deliberate alteration of human or other beings. In many comic book series, genetic engineering is sometimes used as a "plausible" explanation for superhuman powers or abilities.